Sea Snail

Conus striatus (public domain)

Sea snails are marine gastropods. In contrast to sea slugs, they typically have coiled shells. Syrinx aruanus, the largest living sea snail, reaches 91 centimeters (36 inches) in length. Most sea snails do not pose a threat to divers. However, the venomous tooth of some cone snail species can be dangerous and even fatal. In severe cases victims have suffered muscle paralysis, changes in vision, and respiratory failure. The tooth can penetrate neoprene.

skull and crossbones
Some species venomous.

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This supplemental online resource accompanies the book Scuba Diving Hand Signals by Lars Behnke, available on Amazon.